Air filtration arrangement and method

ABSTRACT

Constructions and methods are described for collecting particulate material from gas streams. In certain specifically described air filter arrangements, a first, rigid, filter construction is used in conjunction with a removable and replaceable depth media filter, to form filter media. The preferred arrangement is configured so that the removable and replaceable depth media filter can be removed and replaced, without disengaging the first filter construction from a filter assembly or housing, if desired. Some preferred configurations and materials are described.

CROSS-REFERENCE TO PARENT AND CLAIM OF PRIORITY

This application is a divisional of U.S. patent application Ser. No.08/426,220, filed Apr. 21, 1995, now U.S. Pat. No. 5,669,949 whichapplication is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to filter arrangements. More specifically,it concerns arrangements for filtering particulate material from gasflow streams, for example air streams. The invention also concernsmethods for achieving relatively efficient removal of particulatematerial from gas flow streams.

RELATED U.S. PATENTS AND APPLICATIONS OWNED BY THE ASSIGNEE

The present application is owned by the Assignee (Donaldson Company,Inc.) of U.S. application Ser. No. 08/062,268 filed Dec. 22, 1994, nowU.S. Pat. No. 5,423,892, which is a divisional of Ser. No. 07/897,861filed Jun. 12, 1992 and issued as U.S. Pat. No. 5,238,474. U.S. Ser. No.07/897,861 is a continuation-in-part of Ser. No. 07/759,445 filed Sep.13, 1991, now abandoned, continued as U.S. Ser. No. 08/025,893 on Mar.3, 1993 and issued as U.S. Pat. No. 5,364,456. U.S. Ser. No. 07/759,445is a divisional of Ser. No. 07/601,242 filed Oct. 19, 1990 and nowissued as U.S. Pat. No. 5,082,476. U.S. Pat. Nos. 5,082,476; 5,238,474;and 5,364,456 are incorporated herein by reference. Many of theprinciples of these patents can be applied in systems according to thepresent invention.

BACKGROUND

Air and gas streams often carry particulate material therein. In manyinstances, it is desirable to remove some or all of the particulatematerial from the gas flow stream. For example, air intake streams toengines for motorized vehicles or power generation equipment, gasstreams directed to gas turbines, and air streams to various combustionfurnaces, often include particulate material therein. The particulatematerial, should it reach the internal workings of the variousmechanisms involved, can cause substantial damage. It is thereforepreferred to remove the particulate material from the gas flow upstreamof the engine, turbine, furnace or other equipment involved.

In other instances, production gases or off gases from industrialprocesses may contain particulate material therein, for example thosegenerated by the process. Before such gases can be, or should be,discharged through various downstream equipment and/or to theatmosphere, it may be desirable to obtain substantial removal ofparticulate material from those streams.

A variety of air filter or gas filter arrangements have been developedfor particulate removal. For reasons that will be apparent from thefollowing descriptions, improvements have been desired for arrangementsdeveloped to serve this purpose.

A general understanding of some of the basic principles and problems offilter design can be understood by consideration of the following typesof systems: a paper filter; a pleated paper filter; and, a constantdensity depth filter. Each of these types of systems is known, and eachhas been utilized.

Consider first a paper element, comprising a porous paper filteroriented perpendicularly to a gas stream having particulate materialentrained therein. The filter paper selected will typically be onepermeable to the gas flow, but of sufficiently fine porosity to inhibitthe passage of particles no greater than a selected size therethrough. Asimple, planar, filter construction made from such a material could inoperation be oriented completely across the gas flow stream, for examplebetween a source of air and an intake manifold for an engine. As thegases pass through the filter paper, the upstream side of the filterpaper will receive thereagainst selected sized particles in the gasstream. The filter will act to remove the particles from the gas stream.The particles are collected as a dust cake, on the upstream side of thepaper filter.

A simple filter design such as that described above is subject to atleast two major types of problems. First, a relatively simple flaw, i.e.rupture of the paper, results in complete failure of the system, andthus lack of protection of downstream equipment. Secondly, particulatematerial will rapidly build up on the upstream side of the filter, as athin dust cake or layer, eventually substantially occluding the filterto the passage of gas therethrough. Thus, such a filter would beexpected to have a relatively short lifetime, if utilized in anarrangement involving in the passage of large amounts of gastherethrough, with substantial amounts of particulate material above the"selected size" therein; "selected size" in this context meaning thesize at or above which a particle is stopped by, or collects within, thefilter.

The filter lifetime, of course, would be expected to be related to thesurface area of the paper filter, the rate of gas flow through thesystem, and the concentration of particles in the carrier stream. Forany given system, the "lifetime" of a filter is typically definedaccording to a selected limiting pressure drop across the filter. Thatis, for any given application, the filter will have reached its lifetimeof reasonable use when the pressure buildup across the filter hasreached some defined level for that application.

An alternative design to that described above is a pleated paper filter.The arrangement of the filter paper in a pleated configuration generallyincreases the surface area of filter media provided within a givencross-sectional area or volume of space. It will also tend to increasethe strength of the system. Thus, the operating lifetime of the filteris increased, due to the increase of surface area for entrainment ofparticulate material thereagainst. However, pleated paper media is stilla surface loaded filter media. As a thin layer of particulate materialcollects on the upstream surface of the filter element, the filter willstill tend to become occluded. Thus, the lifetime of such a filter isstill relatively short, in applications. In addition, the system isagain subject to significant problems should a minor flaw or rupturedevelop in the paper element.

It is noted that in many applications, the gas stream to be filtered canbe expected to have particulate material of a variety of sizes therein,and/or the equipment can be expected to be subjected to varying gas flowstreams with respect to particulate content. Consider, for example, afilter arrangement designed for utilization in motorized vehicles. Itwill be preferred that the filter arrangements utilized for suchvehicles be capable of filtering out particles ranging from submicronsizes up to 100 microns. For example, vehicles utilized in off-roadcircumstances, at construction sites or at other sites (country roadsperhaps) where a lot of dirt is carried in the air, can be expected toencounter gas streams carrying a substantial percent of about 10 to 100micron material. Most of the air which passes through the air filter ofan over-the-highway truck or automobile, when the vehicle does notencounter dust storms or construction sites, generally carriesrelatively little particulate material above about 5 microns in size,but does carry a substantial portion of submicron to 5 micron sizedmaterials. A city bus, on the other hand, principally encounters onlysubmicron sized carbon particles in the gases passing into the filterthereof. However, even city buses can be expected to at leastoccasionally encounter air having larger particles therein.

In general, filters designed for vehicles should preferably be capableof providing substantial protection to the engine for particlesthroughout a size range of submicron to 100 microns, regardless of whatare expected to be the preponderant working conditions of any specificvehicle. That is, such arrangements should be developed such that theydo not rapidly occlude, under any of a wide variety of conditions likelyto be encountered during the lifetime of the vehicle. Such is true, ofcourse, for any filter system. However, with respect to vehicles, theproblem is exacerbated by the fact that the vehicle moves fromenvironment to environment, and thus can be expected to encounter arelatively wide variety of conditions. A "flexible" arrangement ispreferred at least in part so that one construction of filter can be putto use in a relatively wide variety of applications.

Consider again the paper filter and pleated filter arrangementsdescribed above. A paper filter will relatively rapidly occlude, i.e.reach its lifetime through buildup of filter cake and generation oflimiting differential. Thus, a given filter paper construction would notbe expected to be a very effective system for filtering air under a widevariety of applications, especially with expectation of a relativelylong lifetime. In addition, as explained above, paper filterarrangements do not in general provide good protection, in the event offailure. That is, even a minor rupture or tear can result in a nearlycomplete system failure.

In many applications, an alternative type of filter, generally referredto as a "depth" filter, is available. A typical depth filter is a thicklayer or web of fibrous material referred to as "depth media." Depthmedia is generally defined in terms of its porosity, density or percentsolids content. Typically, it is defined in terms of its solids contentper unit volume, for example a 2-3% solidity media would be a depthmedia mat of fibers arranged such that approximately 2-3% of the overallvolume comprises the fibrous material (solids), the remainder being airor gas space. Another useful parameter for defining depth media is fiberdiameter. If percent solidity is held constant, but fiber diameter isreduced, pore size reduces; i.e. the filter becomes more efficient andwill more effectively trap smaller particles.

A typical conventional depth media filter is a deep, relatively constant(or uniform) density, media, i.e. a system in which the solidity of thedepth media remains substantially constant throughout its thickness. By"substantially constant" in this context, it is meant that onlyrelatively minor fluctuations in density, if any, are found throughoutthe depth of the media. Such fluctuations, for example, may result froma slight compression of an outer engaged surface, by a container inwhich the filter is positioned.

A problem with constant or uniform solidity depth media systems, is thatthey are not readily adapted for efficient filtering under circumstancesin which air or gas flow with varying populations of particle sizes arelikely to be encountered. If the percent solidity of the depth media issufficiently high, relatively large particles will tend to collect inonly the outermost or most upstream portions of the media, leading toinefficient utilization of the overall media depth. That is, under suchcircumstances the particles of solids (especially larger ones) tend to"load" on the front end or upstream end of the media, and do notpenetrate very deeply. This leads to premature occlusion or a shortlifetime. By "premature" in this context, it is meant that although thedepth media volume is large enough for much greater "loading" of solids,occlusion results because the load is heavily biased toward the frontend, and results in blockage (and early pressure differential increase).

If, on the other hand, relatively low density depth media is utilized, agreater percent of its volume will tend to be loaded or filled by largerparticles, with time. This may occur, for example, throughredistribution as particle agglomerates initially formed in moreupstream regions, break up and redistribute inwardly. Thus, at the"lifetime" or "limiting pressure differential" load would be more evenlydistributed through the media depth (although completely uniformdistribution is unlikely). However, very large and very small particleswould be more likely to have passed completely through such a system.

From the description, it will be apparent that constant density depthmedia is not particularly well suited for circumstances in which either:the population of particle sizes within the air flow extends over arelatively wide range; and/or, the air filter is likely to encounter avariety of air streams (conditions) presenting therein a variety ofparticle size distributions.

Very low density depth media, on the order of about 1-3%, and moretypically about 1-2% solidity, is sometimes referred to as "high loft"media. Such media has been utilized as filter media in HVAC filters(heat, ventilation, air conditioning).

The term "load" and variants thereof as used above and referred toherein in this context, refers to amount or location of entrainment orentrapment of particles by the depth media filter.

As explained above, as the density (i.e. percent solidity) of the depthmedia is increased, under constant load conditions, after use the filterwill tend to include a greater load toward the upstream side. Should theload conditions comprise air having a variety of particle sizes therein,or should the filter need to operate under a variety of conditions ofuse, no single density depth media has, in the past, been as effectiveas may be desired, as a filter. That is, for any given percent solidsdepth media, the load pattern will differ depending upon the particlesize distribution within the air or gas stream to be filtered. Thus,while the filter depth could be optimized for one particular particlesize, it might not be sufficient for operation under a variety ofconditions or with gas having a variety of particle sizes therein.

SUMMARY OF THE INVENTION

According to the present invention, an air filter arrangement isprovided. The air filter arrangement generally includes a first filterconstruction having filter media with an upstream side; and, a removableand replaceable filter of depth media operationally positioned incovering relation to the first filter construction upstream side. In apreferred embodiment shown, the first filter construction is an innerfilter construction and the arrangement is configured with the filtermedia of the inner filter being received within the removable andreplaceable filter. In this preferred embodiment, preferably theremovable and replaceable filter is a sleeve filter. In this and similarcontexts, the term "operationally" is meant to refer to orientation foroperation in ordinary use, to filter.

In certain preferred applications, the removable and replaceable filterincludes more than one layer of depth media therein. In preferredconfigurations, the removable and replaceable filter is substantiallycylindrical and includes a first open end for insertion of the innerfilter construction therein, and a second end with an end skirt at leastpartially enclosing the second end. The end skirt may comprise a heatformed ring of flexible polymeric material.

Preferably the sleeve filter comprises a compressible sleeve of depthmedia having a cylindrical configuration and sufficient elasticity andmemory to rebound to its cylindrical configuration when folded ordeformed from cylindrical, under light hand pressure. By this it is notmeant that the arrangement necessarily cannot be irreversibly deformedby hand, but rather that under hand pressure the arrangement can beeasily squeezed, collapsed or rolled in such a manner that it willspring back from that, to re-form the cylindrical sleeve. Sucharrangements will be particularly convenient for handling, storage andshipping.

In certain embodiments, preferably the inner filter comprises a pleatedpaper filter. It may preferably comprise oil pleated paper.

In those arrangements wherein the inner filter comprises a pleated paperfilter, preferably the inner filter includes an outer liner immediatelyupstream from the pleated paper filter. The outer liner may comprise avariety of materials, for example polymeric scrim or a rigid porousmetal liner.

In certain preferred arrangements, the inner filter includes an open endcap and a closed end cap. In those embodiments wherein the removable andreplaceable filter is a sleeve which fits over the inner filter, and theinner filter includes an open end cap and a closed end cap, it willgenerally be preferred that the closed end cap is formed from arelatively hard, smooth material which will present a relatively lowcoefficient of friction or resistance to the sleeve filter slidingthereover. A preferred material for this end cap is a hard urethanematerial having a hardness of at least about 30 Shore D, or a similarhard, smooth, plastic such as plastisol.

The open end cap, in typical arrangements such as those shown in thedrawings, is not necessarily subject to the preference for the lowcoefficient of friction with the sleeve filter, since no substantiallength of the sleeve filter has to slide past the open end cap in use.Indeed, it may be preferred to make the open end cap from a relativelysoft polymeric material, if a radial seal arrangement is desired. Whensuch is the case, preferably the soft polymeric material is apolyurethane foam, and the first end cap includes means for forming aradial seal with the housing.

A preferred configuration for an annular rim of the open end cap isprovided. The configuration includes a seal ramp and sealing shoulder,to advantage.

In certain applications of the present invention, an overall air filterarrangement including a housing is provided. The housing in certainpreferred applications is configured so that the sleeve can be removedand replaced, without dismounting the inner filter from the arrangement.This can be accomplished, for example, with the housing having an endcover oriented in covering relation to an end skirt of the sleevefilter. The housing may comprise a variety of materials, for examplesheet metal or plastic.

Also according to the present invention, a removable and replaceablefilter, for use in air filter assemblies according to the presentinvention, is provided. Further, methods of filtering air, to advantage,are provided.

In one embodiment described herein, the arrangement includes an outerrigid filter and a removable and replaceable inner filter element, ofdepth media. Preferably the inner filter element of depth mediacomprises more than one layer of depth media, most preferably with agradient for filtering efficiency therein. Preferably the inner filterelement is readily collapsible under hand pressure, and is of a materialwhich can readily reform its uncollapsed configuration, when the handpressure is released.

In the drawings, relative component sizes and thicknesses may be shownexaggerated, for clarity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is perspective view of an internal filter element according tothe present invention, and usable in certain assemblies according to thepresent invention.

FIG. 2 is a cross-sectional view of the arrangement shown in FIG. 1;FIG. 2 being taken along line 2--2 thereof.

FIG. 3 is a perspective view of a sleeve component according to thepresent invention; the sleeve component of FIG. 3 being usable incertain overall arrangements or assemblies according to the presentinvention.

FIG. 4 is a cross-sectional view taken generally along line 4--4, FIG.3.

FIG. 5 is an exploded perspective view of an assembly of the internalelement of FIG. 1 and the sleeve of FIG. 3.

FIG. 6 is a fragmentary cross-sectional view of the arrangement shown inFIG. 5; FIG. 6 being taken along line 6--6 thereof.

FIG. 7 is a bottom end view of the arrangement shown in FIG. 5.

FIG. 8 is a fragmentary view of an air filter arrangement incorporatingcomponents according to the present invention; FIG. 8 including portionsbroken away and depicted in cross-section, to show internal detail.

FIG. 9 is a fragmentary, schematic, cross-sectional view of amulti-layered depth media containing sleeve filter, useable inarrangements according to the present invention.

FIG. 10 is a cross-sectional view of an alternate filter constructionaccording to the present invention, with a removable and replaceabledepth media filter positioned inside of another filter element.

FIG. 11 is a fragmentary schematic depiction of a process of forming anend skirt in certain filter sleeves according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Brief Characterization of Related Disclosures Owned by the PresentAssignee

Attention is directed to U.S. Pat. Nos. 5,238,474; 5,082,476; and5,364,456, the disclosures of which are incorporated herein byreference. These patents issued to the assignee of the presentinvention, Donaldson Company, Inc. of Minneapolis, Minn. In thesepatents, arrangements were described in which both depth media andpleated paper media were utilized in the same construction. In theexamples provided, the filter elements included end caps having apleated paper element extending therebetween. In some variations, forexample FIG. 10 of U.S. Pat. No. 5,238,474, a removable upstream regionof depth media was shown around the filter element. Arrangementsincluding more than one layer of depth media, with preferred gradientsin filtering efficiency, were shown.

Some Concerns with Conventional Filters

Some of the advantages of arrangements according to the presentinvention will be understood by consideration of conventional filterarrangements and arrangements described herein, when used as truckengine air filters. It will be understood, however, that applications ofarrangements and principles according to the present invention, may bein a wide variety of equipment or engine uses, not just with trucks.

In general, truck air filter arrangements include filter elements thatperiodically are changed. In general, an air filter arrangement hasreached its design lifetime, when a (design) limiting pressure dropacross the filter media is reached. During use, as particulate materialloads on the filter, the filter increasingly resists gas flowthereacross. That is, the pressure drop across the filter tends toincrease. For any specific application, the "limiting" pressure dropwill the point at which the filter needs to be, or should be, changed.For example, if the filter is being used as an air filter for an intakemanifold of a truck, a pressure drop of about 20-30 inches of water willtypically be the limiting pressure drop. For an automobile, typicallyabout 20-25 inches of water will be the limiting pressure drop. Inindustrial ventilation systems, typically about 3 inches of water is thelimiting pressure drop; and, for gas turbines, typically about 5 inchesof water will be the limiting pressure drop. In some industries orapplications, limiting pressure drops are set in specificationsapplicable to the system, or through regulatory control.

In practice, the pressure drop is not always measured and replacement ofthe filter element does not always occur only when a designated (design)pressure drop is reached. For example, the majority of truck enginefilters are probably serviced on a regularly scheduled basis, typicallydefined by mileage, such as every 30,000 miles or every 40,000 miles.This means that the filter element may be removed and disposed of longbefore its useful life has been expended. It is estimated that, on theaverage, more than one-half of filter element life in trucks is lost bypremature but scheduled servicing.

The consequences of premature servicing extend far beyond mere cost indollars of lost filter life. Conventional truck engine filters containsignificant amounts of raw material, including structural metalcomponents, end cap materials, gaskets, and filtration media. There areconcerns with the impact of disposing these items in landfill, and itwould be preferred to extend lifetime and limit frequency of disposal.Further, even if the filter elements have been used to their usefullife, there may still be portions of them which would be functional andusable, but for the fact that they are inseparably incorporated into asystem which includes "loaded" media.

Another problem with conventional systems, especially those which haveno internal safety filter, i.e. trucks for city use or long haulover-the-highway trucks, is that as the filter element is beingreplaced, the clean air plenum or intake is exposed to the environment.Thus, dirt or other matter can fall into the open air intake, and causeinternal damage to the engine.

Also, premature filter servicing wastes labor hours involved in removingthe used elements, cleaning the air cleaner housings, and installing thenew filters.

Further, it is generally known that "new" filters pass more particulatesthan filters which have been in place for a period of time. This isbecause the particulates that are eventually "loaded" into the filter inuse, facilitate the efficiency of the filtering process. Thus, it is notdesirable to replace partially loaded filter elements prematurely, ifpossible, since they may be at a point in their lifetime when they areoperating more efficiently as a filter than when they are replaced withnew elements.

Detailed Description of the Drawings

An arrangement according to the present invention is depicted in FIGS.1-8. In FIG. 8, the filter element is depicted fully assembled, in anair cleaning arrangement or apparatus. The filter element of preferredarrangements according to this embodiment of the present inventioncomprises two components. These are a first (for the embodiment shown inFIGS. 1-8, internal) typically end-capped, filter; and, an upstream (forthe embodiment shown in FIGS. 1-8, external or outer) removable andreplaceable filter (for the preferred embodiment shown, a sleevefilter). In FIGS. 1 and 2 an internal or safety element is shown. InFIGS. 3 and 4, the removable and replaceable filter sleeve, whichoperates as a primary filter element, is depicted. In FIGS. 5-7, anassembled filter element, comprising the internal element and theremovable and replaceable sleeve, is shown. In this context, the term"removable and replaceable" is meant to refer to a filter mediacontaining component that can be removed from the remainder of thefilter element and be replaced. That is, in this context the term is notused in reference to the fact that, of course, the entire filter element(comprising both the sleeve and the safety element) can be removed froman air cleaner and be replaced. Rather, it is used to describe theseparability of the upstream filter component (for example the sleeve)from the downstream filter component (for example the inner filter).

Referring to FIG. 1, the reference numeral 1 generally designates apreferred internal filter element or cartridge, according to the presentinvention. The internal element 1 is rigid and includes first and secondopposite end caps 3 and 4, with filter media 6 extending therebetween.In the arrangement shown, internal element 1 includes an inner liner 8and an outer surface or liner 9. A variety of materials may be utilizedfor the inner and outer liners 8 and 9. For the particular arrangementshown, the inner liner 8 comprises a porous metal liner or expandedmetal liner, and the outer liner 9 comprises scrim 10, i.e. a fibrousweb of material.

Still referring to FIG. 1, for the particular arrangement shown,internal element or cartridge 1 comprises a generally cylindricalconstruction defining an inner or internal chamber or bore 11 withopposite ends. End cap 3 is an open end cap, and thus includes bore 12for air flow communication from internal bore 11.

In contrast to end cap 3, in the particular embodiment depicted, end cap4 is a closed end cap (FIG. 2). That is, it does not include a boretherein, rather it provides a closed end or cover 13 over an end of bore11.

For the particular arrangement shown in FIG. 1, filter media 6 comprisespleated paper media 15 arranged in a cylindrical pattern and with thepleats aligned longitudinally. In some embodiments, the preferredpleated paper media 15 is an oiled media. In many applications arelatively short pleat depth, for example about 0.375 to 0.81 inches,may be used. Media 6 may include alternate media or additional media, to(oiled) pleated paper. It may include, for example, depth media and/oran agglomerating filter.

The particular internal element or cartridge 1 depicted is a "radialseal" cartridge. This will be understood from consideration of FIG. 8,described below. In general, this means that element 1 is sealed, withan air intake conduit of an engine, by radial engagement along surface16 in end cap 3. By "radial", in this context, it is meant that thecompressive forces for sealing are directed radially about alongitudinal axis 18 of element 1, rather than axially (axially being inthe direction of extension of longitudinal axis 18). Features accordingto the present invention may be utilized in axially sealing systems.However, it is an advantage of arrangements according to the presentinvention that they can be readily incorporated in, and used in, radialsealing systems. Radially sealing systems are disclosed, for example, inU.S. Pat. No. 4,720,292, the disclosure of which is incorporated hereinby reference.

Still referring to FIG. 1, outer surface 20 of end cap 3 may befeatureless, or may include thereon various features to facilitateassembly. For the particular arrangement shown, surface 20 includesprojections or bumpers 21. These may be used to facilitate assembly andmaintenance of a desired position within a housing, FIG. 8.Alternatively, or in addition, surface 20 may include axial seal ringsor beads thereon.

For the arrangement of FIGS. 1-8, the preferred end cap material forforming end cap 3 in inner element 1, when a radial seal arrangement isinvolved, includes the following preferred polyurethane, processed to anend product (soft urethane foam) having an "as molded" density of 14-22pounds per cubic foot (lbs/ft³) and which exhibits a softness such thata 25% deflection requires about a 10 psi pressure. The preferredpolyurethane comprises a material made with I35453R resin and I3050Uisocyanate. The materials should be mixed in a mix ratio of 100 partsI35453 resin to 36.2 parts I3050U isocyanate (by weight). The specificgravity of the resin is 1.04 (8.7 lbs/gallon) and for the isocyanate itis 1.20 (10 lbs/gallon). The materials are typically mixed with a highdynamic shear mixer. The component temperatures should be 70°-95° F. Themold temperatures should be 115°-135° F.

The resin material I35453R has the following description:

(a) Average molecular weight

1) Base polyether polyol=500-15,000

2) Diols=60-10,000

3) Triols=500-15,000

(b) Average functionality

1) total system=1.5-3.2

(c) Hydroxyl number

1) total systems=100-300

(d) Catalysts

1)amine=Air Products 0.1-3.0 PPH

2) tin=Witco 0.01-0.5 PPH

(e) Surfactants

1) total system=0.1-2.0 PPH

(f) Water

1) total system=0.03-3.0 PPH

(g) Pigments/dyes

1) total system=1-5% carbon black

(h) Blowing agent

1) 0.1-6.0% HFC 134A.

The I3050U isocyanate description is as follows:

(a) NCO content--22.4-23.4 wt %

(b) Viscosity, cps at 25° C.=600-800

(c) Density=1.21 g/cm³ at 25° C.

(d) Initial boiling pt.--190° C. at 5 mm Hg

(e) Vapor pressure=0.0002 Hg at 25° C.

(f) Appearance--colorless liquid

(g) Flash point (Densky-Martins closed cup)=200° C.

The materials I35453R and I3050U are available from BASF Corporation,Wyandotte, Mich. 48192.

The material from which end cap 4 is formed is preferably a differentmaterial than the soft polyurethane material used in end cap 3, when endcap 3 is formed from a soft polyurethane foam for use in generating aradially sealing element. A reason for this is that relatively softpolyurethane foam typically has a rubbery surface texture whichgenerates a relatively high coefficient of friction with respect tosliding other materials thereacross. In certain preferred arrangementsof the invention, as described hereinbelow, the outer filter is a sleevefilter which slides snugly over end cap 4, during assembly. It would bepreferred that the coefficient of friction between the end cap 4 and thesleeve element be relatively low. This can be facilitated by avoidinguse of a soft polyurethane foam material for end cap 4.

Preferably, the material from which end cap 4 is formed is a relativelyhard, smooth material. If it is a polymeric material, preferably it is ahard polyurethane. Polyurethanes formed from commercially available WUC36081R (resin) and I3050U (isocyanate), both available from BASF, can beused for this end cap. Thus, certain preferred arrangements according tothe present invention have a relatively unique construction whereindifferent materials are utilized for the opposite end caps, toadvantage. It will be understood that preferably in each instance, thematerial is one which can be molded with the filter material 6 of theinternal element 1 potted or embedded therein, and extending between thetwo end caps 3 and 4.

In general, the use of scrim 10, rather than an expanded metalconstruction, for liner 9 will also facilitate assembly. Expanded metalliners include burrs which may tend to catch on media slidingthereacross.

Attention is now directed to FIG. 2, in which the arrangement of FIG. 1is shown in cross section. From FIG. 2, it will be understood thatfilter media 6 includes opposite ends 23 and 24, embedded in end caps 3and 4, respectively. Further, liners 8 and 9 include opposite ends, alsoembedded in end caps 3 and 4.

End cap 3 includes an outer annular surface 26 with various featuresthereon and shoulder 27. In particular, and referring to FIG. 6, surface26 includes particular, and referring to FIG. 6, surface 26 includesbeveled region or sealing ramp 28, and second outer (axial) shoulder 29.Surface 26 further includes annular surface 30, between beveled region28 and second shoulder 29. In this context the term "axial" refers to ashoulder oriented to be abutted by an item under a force directed along,i.e. in the direction of, axis 18.

The features of outer annular surface 26 facilitate engagement with theouter, removable and replaceable, sleeve filter. This will be understoodfrom the descriptions below with respect to FIGS. 5, 6 and 7.

Referring again to FIG. 2, end cap 3 further includes inner compressiblering 32 occupying a volume between surface 16 and a portion of innerliner 8. Ring 32 is appropriately sized and configured to generate adesirable radial seal. Surface 16 is preferably stepped, as shown at 33,to facilitate sealing.

Attention is now directed to end cap 4, FIG. 2. End cap 4 generallyincludes an outer surface 35 including peripheral ring 36. The end cap 4further includes annular ring 37. For the particular embodimentdepicted, surface 38 of annular ring 37 is generally featureless exceptfor inner shoulder 40, rounded outer shoulder 41 (and any standoffs, notshown, resulting from the molding process). Advantages from thesefeatures will be apparent from the descriptions with respect to FIGS.5-7.

Attention is now directed to FIGS. 3-5. Reference numeral 50, FIG. 3,generally designates an outer, removable and replaceable, sleeve filtersized and configured to be positioned over internal element or cartridge1, in use. With the particular arrangement shown, outer sleeve 50includes generally cylindrical outer surface 51, internal bore 52,insert end 53, and radial end flange or end skirt 54.

Still referring to FIG. 3, the particular sleeve 50 depicted, comprisesfour layers 55, 56, 57 and 58 of depth media. As will be understood fromdescriptions hereinbelow, variations in the number of layers can beused. The particular layers 55, 56, 57 and 58 shown provide for apreferred gradient in efficiency for trapping particles. Each of layers55, 56, 57 and 58 comprises a generally cylindrically wrapped sheet ofdepth media. In FIG. 3, a seam 59 is depicted in each layer. Attachmentat seams 59 can be provided by a contact adhesive such as 3M Super 77(available from 3M Company, St. Paul, Minn.). Alternatively, or inaddition, heat sealing may be used.

Referring to FIGS. 5, 6 and 7, in use, the particular outer sleeve 50shown is slid over internal element 1 (i.e. through insert end 53),preferably until end skirt 54 approaches (and preferably even abuts)surface 35 of end cap 4, FIG. 7. Thus, in use, filter media 6 ofinternal element 1 will be positioned within internal bore 52 of outersleeve 50, and will be overlapped (upstream) by all layers of depthmedia in sleeve 50, i.e. layers 55, 56, 57 and 58.

For the particular arrangement shown in the drawings, no separatemechanical attachment mechanism is used to secure outer sleeve 50 inposition over internal element 1 other than a relatively snug fit. Ingeneral, it is foreseen that the outer layer(s) of sleeve 50 that slideover ramp 28 to abut shoulder 29 will be made from flexible fibrousmaterial having sufficient elasticity and memory, to ensure a snugengagement when stretched over surface 30, FIG. 6. Indeed, typicallyouter sleeve 50 will comprise, at least in outer layers thereof,cylindrically configured fibrous depth media, which possesses suchproperties.

Referring to FIG. 4 for the preferred embodiment shown, as previouslyindicated, outer sleeve 50 comprises a multi-layer depth mediaarrangement 60. The particular sleeve 50 shown includes outer layer 55and three inner layers 56, 57 and 58. Variations in fiber diameter,density and/or thickness between or among the various layers can be usedto provide preferred loading characteristics, filter efficiency andfilter performance. Indeed, variations in the number of layers can beused. Principles related to this are provided hereinbelow.

Attention is now directed to FIG. 6, which shows outer sleeve 50 mountedon internal element 1, in cross-section. Attention is focused on theportion of the drawing whereat insert end 53 of outer sleeve 50 is shownengaging end cap 3 of internal element 1. In particular, ends 65 and 66of the outer two layers 55 and 56 (in sleeve 50) are expanded overbeveled ramp 28 in end cap 3 and sit against outer shoulder 29 and outerannular surface 30. Thus, ends 65 and 66 include an expanded (internal)diameter portion 67 sized and configured for an interference fitengagement with annular surface 30. It is noted that for typicalapplications, it will not be necessary to further seal the engagementbetween end cap 3 and outer sleeve 50 at this location, since a snug fitbetween the two will generally be enough, given the protection affordedby filter media 6. In general, what is preferred is a sufficientinterference fit to keep sleeve 50 snugly fit against end cap 3, so thatair passing therebetween, and not obtaining the benefit of passagethrough some of the depth media, is held to a minimum, or at least tobelow an undesirable level. In general, it is believed this can beaccomplished if the outer layer(s) of media, which is (are) expandedover ramp 28 is (are) made from a stretchable polymeric material, suchas air laid polyester fiber materials, and is (are) expanded at leastabout 1% in circumference or diameter, when slid over the ramp 28. Theminimum figure of 1% is believed sufficient for typical truckinstallations, which will involve designs wherein the end cap 3 outerdiameter at surface 30 is about 4.5 to 13 inches.

Attention is now directed to inner layers 57 and 58, FIG. 6. Inparticular, attention is directed to ends 70 and 71 of inner layers 57and 58. Ends 70 and 71 are not long enough to stretch over ramp 28.Thus, ends 70 and 71 are not stretched or expanded substantially.Indeed, in some instances, since layers 57 and 58 are similarlypositioned layers, and do not need to expand substantially in use, theymay be made from a material, or may have scrim attached to them, whichis relatively non-expandable. This will be further understood fromdescriptions given below. In general, a layer of scrim along the insidediameter of innermost layer 58 will be preferred, to facilitate slipbetween the sleeve 50 and inner element 1, during assembly anddisassembly.

Attention is now directed to end skirt 54, FIG. 7. In general, end skirt54 comprises a ring at end 72 of outer sleeve 50. For the embodimentshown, end skirt 54 is positioned to be pressed against end cap 4, whenouter sleeve 50 has been properly positioned on internal element 1.Generally, end skirt 54 will comprise a skirt of the same fibrousmaterial from which at least outer layers 55 and 56 are formed, exceptmelted and collapsed (crushed). A procedure for this is described belowin association with FIG. 11.

Attention is now directed to FIG. 8. Reference numeral 80, FIG. 8,generally designates an assembled air filter arrangement according tothe present invention. In FIG. 8, portions are broken away to showinternal detail. The air filter arrangement 80 of FIG. 8 is a "normal"or "forward" flow arrangement. That is, in normal operation flow of airto be filtered is shown in the direction of arrows 81; i.e. through thefilter media from the outside in.

In general, air filter arrangement 80 includes housing 83; downstream,internal, element 1; and, upstream outer sleeve 50. Housing 83 includesouter wall 84, inlet 85, cover 86 and outlet tube 87. For thearrangement shown, cover 86 is generally openable, and in fact isremovable and replaceable from outer wall 84, for access to theinternally received internal element 1 and outer sleeve 50. In general,engagement between cover 86 and a remainder of housing 83 is provided bybolts 90. Preferably the arrangement is sized so that cover 86 willpress skirt 54 against internal element 1. This will help secure sleeve50 in position and provide the non-critical seal between sleeve 50 andend cap 3.

Outer wall 84 defines a space 92 around outer sleeve 50 so that air tobe filtered can pass efficiently into outer sleeve 50 throughout itscircumference.

In general, outlet tube 87 includes inner section 95 with rim 96. Rim 96is preferably circular and of an appropriate diameter so that, wheninserted within bore 12 of end cap 3, a radial seal (at 98) with surface16 will be formed. Arrangements suitable for accommodating this aredescribed, for example, in U.S. Pat. No. 4,720,292, incorporated hereinby reference. In general, at least about 20-25% compression of some ofthe material in ring 32, between and against surface 16 and liner 8,will be preferred, for a good radial seal.

For typical radial sealing arrangements such as the one shown in FIG. 8,the internal length of housing 83, i.e. the distance between surface 100and cover 86, need not necessarily be designed to apply substantialaxial forces to the various portions of the elements received therein.This is because the radial seal provides for sealing, and axial forcesare not essential to its maintenance. Some axial compression, however,may be desired in such radial seal systems to provide protection againstleaks developing as the arrangement is bounced or jostled in use. Indeedin some systems involving radial seals, even auxiliary axial seal ringsmay be desirable.

From a review of FIG. 8, preferred operation will be readily understood.In general, air passing into inlet 85 is dispersed in space 92, andpasses through outer sleeve 50 in the direction of arrow 81. Much of theparticulate material, carried within the air, will be deposited withinthe depth media of filter 50. The air then passes through internalelement 1. Any particulate material to be removed from the air flowstream but not removed from the outer sleeve 50 will generally beremoved by the internal element 1. The clean air then passes throughinner liner 8 and into internal bore 11. It is then passed outwardlyfrom the air filter arrangement 80 through outlet tube 87, and into theair intake of the engine.

When it has been determined that outer sleeve 50 is to be changed, forexample at periodic maintenance or under circumstances in which ameasured level of pressure differential across the filter element hasbeen reached, maintenance is relatively straightforward. End cover 86 isopened, by operation of bolts 90. Outer sleeve 50 can then be readilyslid off internal element 1. Indeed, if desired, for the particulararrangement depicted sleeve 50 can be slid over end cap 4 and removedwithout breaking the radial seal between internal element 1 and outlettube 87. A new sleeve can be readily positioned over internal element 1.After replacement of the cover 86, the air filter arrangement 80 isgenerally ready to be placed back in use. The used outer sleeve can bediscarded. (It is noted that the inner element 1 can be changed by ananalogous procedure.)

For a review of the particular arrangement in FIGS. 1-8, numerousadvantages to some of the possible embodiments of the present inventionare apparent. For example, the particular outer sleeve 50 depicted, doesnot comprise rigid structural features (such as metal, rubber or hardplastic), but rather it only comprises flexible depth media material andflexible fibrous scrim. Since it does not contain rigid end caps, metalstructural elements, etc. it can be very easily collapsed and discarded.Also, much of the spent material is void (except for dust loading), soit does not contribute as substantially to landfill, as many previousarrangements. Further, new sleeves, i.e. replacement sleeves, can beshipped and stored in a "collapsed" configuration; i.e. squeezed orrolled. This provides space saving advantages.

From the description provided above with respect to FIG. 8, it isapparent that it is possible to substantially regenerate the filterelement of the particular embodiment depicted, without removing internalelement 1 from the system. Thus, it is not necessary to expose the cleanair plenum downstream from the filter arrangement to the environment andpossible contamination by dust or dirt. Further, certain structuralfeatures such as the pleated paper filter, the internal liner, and theend caps are not replaced simply because the upstream depth media issubstantially loaded. Rather they remain in place, and it is only thedepth media in outer sleeve 50 which is relatively frequently changed.This facilitates disposal of parts, and reduces waste present inconventional designs. For example, the outer sleeve 50 might be designedto be replaced every 30,000 miles, with the inner filter 1 replaced onlyevery 300,000 miles.

Further, from the description it will be apparent that the maintenanceoperation is relatively simple and straightforward, and thus easier toeffect.

From a review of FIG. 8, it will be seen that in selected embodiments,advantageous use may be made of certain principles according to thepresent invention, with respect to materials and material use. End cap 4may have a smaller diameter than an analogously positioned end cap inprior constructions, since the outside diameter of the end cap does notextend substantially beyond the outside diameter of the inner pleatedpaper material. Indeed, preferably it does not extend more than about0.125 inches beyond the outer liner 9, so that minimal spacing, if any,between the inside layer 58 of the outer sleeve 50, and the liner 9 isinvolved. As a result of having a smaller outside diameter, lessmaterial is sometimes needed for forming end cap 4, relative toconventional systems. This can be used to achieve material savings andprocess advantages. In some instances, a weight savings, at least forthe rigid portions of the filter element, can be made as well.

Selection of Media Characteristics; Principles of Operation

Flexibility obtainable with designs according to the present inventionallows for advantageous application to accommodate filtering needs in awide variety of environments. For example, the outer sleeve 50 can bedesigned to comprise only one type of depth media, more than one type ofdepth media, preferred gradient density arrangements, etc. Differentsleeve elements can be designed for the very same air filter arrangementand equipment, with the choice for use being dependent upon the expectedoperating conditions. Indeed, alternate sleeves can be used dependingupon the particular environment to which the equipment will be exposed;and, the filter sleeve can be changed when the environment changes, ifdesired. Also, different geometric configurations may be used. Forexample, the inner filter might have a circular cross-section while theouter sleeve has an oval cross-section.

In general, attention is directed to U.S. Pat. Nos. 5,238,474, 5,364,456and 5,082,476, with respect to selection of media. Similar principles tothose outlined in these references can be applied with systems accordingto the present invention.

For example, as explained above, uniform or constant density depth mediacan be used in outer sleeve 50. However, improvement over theutilization of constant density depth media can be obtained in manyarrangements, through the utilization of a gradient depth media filtersystem, in outer sleeve 50; that is, an arrangement wherein the depthmedia of outer sleeve 50 is not provided with a constant capability(efficiency) to trap or load solids throughout. This can be done byutilizing a multi-layer arrangement, such as shown in FIGS. 3 and 4, inwhich depth media in at least some of the various layers is selected tobe different. It may alternatively (or in addition) be accomplished byusing the same media in more than one layer but varying the amount ofcompression the media is under, thereby changing its installed (ratherthan free state) solidity.

A preferred gradient depth media system, for the removable andreplaceable upstream filter member, is one in which the efficiency orability to trap particles (especially smaller ones) in general increasesfrom an upstream side toward a downstream side. In typical applications,the efficiency of the depth media is increased by providing anincreasing density (percent solids) gradient. It may also (oralternatively) be accomplished through decreasing fiber size, varyingdepth media thickness, varying compression or with a combination ofthese techniques. By "increase" in "efficiency" or "ability to trapparticles" in this context, it is not meant that the downstream layernecessarily does collect more particles, in use. Rather it is meantthat, if the two layers were tested separately (but in the form andcompression they have in the arrangement), under exposure to teststreams of dust containing small particles (less than about 5 microns),the material which forms the more upstream layer of the two wouldgenerally show less efficiency of trapping, than the material whichforms the inner layer. Alternately stated, the innermost of the layersbeing compared is constructed and arranged to more efficiently trapsmaller particles.

From the above, some variations in filter design according to thepresent invention will be apparent. For example, the preferred designwill be such that much of the dust loading will occur in the removableand replaceable sleeve 50; indeed typically the system will be designedso that the great majority of dust loading (by wt-%) occurs here. Thatis, in typical use, for preferred embodiments there will be relativelylittle dirt, dust or particulate loading on or in the inner filter 1, inuse. Designs can be made to emphasize this. In such arrangements, theinner filter will generally operate as a safety filter and as astructure to hold the depth media of the outer sleeve 50 in place, andresist collapse. This latter is facilitated by the fact that the innerfilter includes rigid structural components that can withstand pressure,typically a design limit of at least 100 inches of water; whereas fortypical preferred embodiments described herein the outer sleeve is amore easily compressible sleeve.

In many preferred arrangements according to the present invention, theupstream removable and replaceable (for example sleeve) filter will bedesigned to operationally collect at least 90% by weight (and in someinstances 95% or more) of the particulates collected in use. By"operationally collect" in this context it is meant that if thearrangement were examined after a substantial period of typical use (forexample 20,000 miles in an over-the-highway truck or city deliverytruck), at least 90% (or in some systems at least 95% ) of theparticulates (by wt.) loaded on the entire system would be found in theremovable and replaceable (sleeve) filter.

The material chosen for the depth media in the outer sleeve 50 can bechosen based upon various needs or design criteria. For example, itmight be selected to be a good storage or loading media. Alternatively,or in addition, a layer may be chosen to operate as a good agglomeratingfilter. An agglomerating filter is a material which facilitates particleagglomeration thereon, and from which the agglomerated particles mayeventually be released to settle into inner layers or filter members.More specifically, an agglomerating filter media has large interfiberdimensions relative to the fiber size and particles being filtered. Asparticles are collected and built up on the fibers, they are unable tobridge the interfiber spaces. These groups of particles may be shed ordislodged from the fibers as agglomerates under the influence of fluiddrag forces or impact of incoming particles. The specific dimensions ofgood agglomerating media depend on the size distributions of theparticles being filtered and existing flow conditions.

As indicated above, a variety of materials can be utilized for formingthe outer layer or liner 9 of inner element 1. As previously indicated,a scrim 10 can be used, bonded to the tip of each pleat. For example, apolyester scrim with a hot melt scrim immediately adjacent can beapplied to the pleat tips, with heat. Such a polyester scrim willgenerally, once in place, help secure the pleat tips in position andavoid undesirable movement in use. This can be readily accommodated by ascrim which is only about 0.004-0.010 inch thick.

Preferred scrim comprises polyester (for example spunbonded) fabrics orpolypropylene fabrics. Such scrim materials are available from ReemayCorporation of Old Hickory, Tenn. 37138, under the trade name REEMAY2011. For the hot melt scrim, applied with the polyester scrim, Bostik2215, available from Bostik, Middleton, Mass. 01949, can be used. Anadvantage to such materials is that they are smooth and free fromundesirable burrs, unlike metal liners.

In some arrangements it may be preferred to utilize, as the scrim,fibrous material having a microfiber applied thereto. This generates amicrofiltration medium, that can operate as a "polishing" filter toadvantage. Techniques for applying polymeric microfibers to substratesare described in U.S. Pat. No. 4,650,506 issued to Donaldson Company,Inc. of Minneapolis, Minn. and incorporated herein by reference.Alternatively glass microfibers might be used. The particular techniquesutilized for applying the microfibers to the substrate are not believedcritical to, or essential to, obtaining many of the advantages accordingto the present invention.

With respect to the scrim 10, techniques described in the U.S.application entitled "PLEATED FILTER AND A METHOD FOR MAKING THE SAME"filed on the same day as the present application, owned by the Assigneeof the present application, and with Francis A. Friedmann; Wayne M.Wagner; and Daniel T. Risch identified as the inventors may be applied,even though the present application concerns air filters. The Friedmannet al application is incorporated herein by reference.

A tight fit between the pleats and the inner liner 8 is also desirable.This will limit pleat movement against the inner liner, and thusminimizes the likelihood that a hole will develop in the pleated paperat this location. The tight fit is facilitated when the material of thescrim 9 is one which, when heat secured to the pleat tips, tends toshrink somewhat. The material REEMAY 2011 accommodates this.

It is foreseen that in some arrangements, the principles according tothe present invention may be applied in axial sealing arrangements.Under such circumstances, at least in some instances, it may bepreferred to have rigid metal liners for both the inner liner 8 and theouter liner 9. This is so that an axial sealing gasket against end cap 3can be positioned "between" the two rigid structural members, i.e., theinner and outer liners 8 and 9, which will carry the axial load. Ofcourse, liner 9 may comprise both a layer of scrim 10 and a metal liner.

Attention is directed to FIG. 9. This figure is a schematic indicating aplurality of layers or stages that are usable in an outer sleeve 50according to the present invention. It should be understood, however,that fewer or more layers may be used, depending upon the particularneeds and design. The purpose of the schematic of FIG. 9 is to provide abasis for discussion of some possibilities.

Assume that the arrangement of FIG. 9 is an outer sleeve of a forwardflow arrangement. Under such circumstances, air flow would generally beagainst the outermost or largest diameter layer, i.e., layer 200, withfiltering flow being directed inwardly. Typically, the arrangement wouldbe designed such that each inner layer is an equal or more efficientfilter than the next outer layer. This does not mean that greaterfiltering actually occurs (in use) with each inner layer, but ratherthat if each were tested separately, it would show a greater efficiencyfor trapping particles, especially ones less than 5 microns. It isforeseen that in most instances, preferred designs will be such thatgreater "load", i.e., percentage of materials trapped by the entiresystem in use, occurs in the outermost layers. That is, the outermostlayers would include at least some material operating as "storage" depthmedia, with a less high efficiency but a substantially greater capacityfor storing filtered material.

Still referring to FIG. 9, the schematic arrangement includes layers200, 201, 203 and 204. From the following discussion of a possiblearrangement for use in developing an over-the-highway truck filter, somegeneral principles for selection of materials and a wide variety of useswill be understood.

For example, in a typical system for use in an over-the-highway truck,the outer layer 200 may comprise a fibrous material, typically anorganic polymer such as polyester. It would preferably have a goodspring rate and compressibility. Desirable characteristics in theoverall sleeve 50 that are preferably enhanced by the physicalproperties of the layer 200 include: an ability to compress (for ease ofshipment or storage) with memory to spring back into shape; and, asubstantial capacity for loading particles therein during filtering. Itis foreseen that in a typical application for an over-the-highway truck,the outer layer would have a thickness of about 0.2-0.75 inches,depending on the particular application and size constraints. Usablematerials include 4.2 ounce/yd² polyester depth media having a solidity(free state) of about 0.8-1.4% , available from Kem-Wove, Inc. ofCharlotte, N.C. 28241, or its performance equivalent. This materialcomprises 40% by weight 6 denier (24 micron) fibers) and 60% by weight1.5 denier (about 12-14 micron) fibers.

In general, useable materials for layer 200 will comprise 3.7-5.0 ozpolyester depth media having % solidity (free state) within the range of0.55-1.4% (typically comprising a blend of fiber sizes within the rangeof 1.5-6.0 denier). Such materials can (and will typically) be usedwithout substantial compression, if desired.

For the particular example provided, the next inner layer 201 is about0.15-0.4 inch thick layer of material having a greater efficiency forfiltering than the next upstream (outer) layer 200, but still includinga substantial capacity for loading or storage of particulates. Onepreferred commercially available material is a polyester material havinga 1.5 denier fiber size (i.e., 12-14 microns), and a percent solidity(free state) about 1.5-1.8%. This commercially available material isKem-Wove 8643. In general, one class of useful materials will comprise3.0-3.9 oz/yd² polyester depth media having a % solidity (free state)within the range of 0.7-1.8% (typically comprising 1.5 denier fibers).

Preferably a contact adhesive is provided between layers 200 and 201, inouter sleeve 50. A spray-on contact adhesive such as 3M Super 77,available from 3M Company, St. Paul, Minn., may be used, to secure thetwo layers to one another and facilitate integrity of the sleeve 50.

If the arrangement in the schematic of FIG. 9 is applied in theparticular embodiment of FIG. 8, it will be understood that the twoouter layers thus far defined (i.e. layers 200 and 201) are the twolayers which are stretched or expanded over the ramp 28, to seal withend cap 3. Thus, they will preferably have been chosen from materialswhich can expand somewhat, and have sufficient memory to retain a snugfit.

In contrast, the inner layers 203 and 204 of FIG. 9, if applied in theembodiment of FIG. 8, would be layers that are not expanded over ramp28, but rather terminate at end cap 3 and are not stretched for a snugfit. These layers then may comprise material which is itself is not verystretchy, or which is secured to a backing or scrim that does notstretch significantly.

Still referring to FIG. 9, for the example described, the inner layer203 comprises a polymeric fiber which is relatively fine and has ahigher filtering efficiency than either layers 201 or 200. In typicalembodiments it will have a thickness of about 0.08-0.3 inches. A usablecommercially available material for layer 203 is AF18 available fromSchuller International Inc. of Denver, Colo. 80217. It is secured tolayer 201 by means of a contact adhesive.

It is foreseen that in some preferred arrangements, both layers 203 and204 will comprise the same material, for example (AF18). It is alsoforeseen that in many preferred arrangements the most downstream(interior) surface of the sleeve 50, indicated in FIG. 9 at 205 willcomprise a scrim, preferably a spunbonded polyester scrim of about0.004-0.010 inches thick. A commercially usable such material is REEMAY2011 which has a weight of 0.7 oz per square yard. A desirable optionsome instances is to utilize a scrim having fine fiber thereon, toprovide some additional filtering protection. Fine fiber technologywhich can be adapted to this use is described in U.S. Pat. No. 4,650,506assigned to Donaldson Company, Inc. of Minneapolis, Minn. In someinstances multi-layers of scrim may be used, especially, for example, toenhance filter efficiency.

In general, an important consideration in selecting materials for thevarious layers is appropriate building of the gradient. While it ispreferred that each layer have an equal or greater efficiency forfiltering, than the next layer upstream; and, preferably, that thesystem include at least three layers having different filteringefficiency; if the gradient between any given two layers is too abrupt,the arrangement is less likely to perform well in meeting its objectivesin use. This is because a relatively abrupt gradient may lead to apremature plugging or loading in the more downstream, more efficient,layers.

In general, the objective of the first stage (most upstream) media is tocollect and store a major portion (e.g. 70-90% by weight) of theairborne particles entering the filter during its intended lifetime. Itssuitability for this purpose is determined by its fiber size, solidityand thickness. Thickness is limited to the portion of the overallthickness that can be allocated to the first stage media, usually about1/2 of the overall thickness. A media that is too high in solidity or oftoo fine a fiber size will be too efficient and plug prematurely. On theother hand, the preferred first stage media should have adequateefficiency to protect the downstream media from plugging prematurelyfrom excessive numbers of particles. A media, found through experienceto satisfy the requirements of the stage one (most upstream) media forthe over-the-highway trucks, is the Kem-Wove 4.2 oz depth media.

The final stage (most downstream) depth media in the removable andreplaceable part of the element is selected to have a high efficiencythat will protect the pleated inner filter from plugging over several(and sometimes up to as many as 10 to 20) changes of the sleeve filter.The final stage media is also selected for its effectiveness (i.e.efficiency and storage capacity) on submicron particles that typicallypenetrate the upstream stages. Media found through experience to satisfythis requirement includes AF18.

Thus, the sleeve filter consists of a multilayered depth media in which:efficiency typically increases from upstream to downstream layers anddust storage capacity typically decreases from upstream to downstreamlayers. The first (most upstream) layers see the greatest quantity ofcontaminant and therefore must have a high dust-holding capacity. Forstate-of-the-art depth filter media, high storage capacity requireslarger fibers (e.g. 12 to 24 microns) and large interfiber spaces (i.e.low solidity). As a result, efficiency of high storage media is limited.Solidity is generally a good indicator of the efficiency and storagecapacity of these larger fiber media.

Because of the prefiltration of upstream layers, particle exposure ofdownstream layers is reduced. Also, as a consequence of the upstreamlayers, downstream layers typically see a finer particle size thanupstream layers. Therefore, higher efficiency depth media (i.e. smallerfibers and/or higher solidity) can be utilized for the downstreamlayers. To achieve the high efficiency required to protect the pleatedinner filter from premature plugging, the final (downstream) layer ofmedia may utilize fibers less than 5 microns in diameter. Solidities ofthese fine fiber media cannot always be compared directly withsolidities of the coarser upstream media.

Because of the inadequacy of solidity as the only measure of performancefor both coarse and fine fiber media, an efficiency measurement has beenused to characterize media for the sleeve filter. The test measuresefficiency of filter media on 0.78 micron polystyrene particles at astandard flow of 20 fpm (feet per minute). In this test neutralizedpolystyrene particles are dispersed into a dry air stream at a lowparticle concentration upstream of a 3 inch diameter test filter. Aparticle counter is used to measure efficiency of the test sample.Because of the speed of the test, several efficiency readings can bemade on different portions of the media. These readings are thenaveraged to determine the media efficiency.

The table below lists the 0.78 micron particle efficiencies of thevarious medias discussed with respect to the present embodiments of thesleeve filter:

    ______________________________________                                                         Efficiency                                                   Media            (percent)                                                    ______________________________________                                        Kem-Wove 4.2 oz   5-6%                                                        Kem-Wove 8643      8%                                                         AF18             10-11%                                                       ______________________________________                                    

In general then, in certain preferred systems: the most upstreamregion(s) of depth media in the sleeve filter is a material which has anefficiency (for 0.78 micron polyester particles under the testconditions) of less than about 6% (preferably 5-6%); the next downstreamregion(s) comprise material which has an efficiency (for 0.78 micronpolyester particles under the test conditions) of 7-9% (preferably about8%); and the next downstream region (preferably the most downstreamregion) is a layer (or layers) of material having an efficiency forfiltering, of such particles, of at least 10%, typically 10-11%. In thischaracterization, the efficiency is with respect to the material testedoutside of the construction.

Formation of End Skirt

Attention is now directed to FIG. 11. FIG. 11 is a schematic depictionof a step of forming an end skirt, such as end skirt 54, in a filtersleeve according to the present invention. Referring to FIG. 11, acylindrically disposed filter media is indicated generally at 300. Themedia 300 includes end sections 301 and 302, of the outer two layerswhich are folded over to form the end skirt. The outer two layers 301and 302 will generally correspond to layers 55, 56, FIG. 3. The innertwo layers and scrim are indicated at 303, 304 and 305 respectively.

In FIG. 11, outer layers 301 and 302 are folded over die 306, and aresecured in die recess 307 by second die 308. In operation, third die309, which is a heated die, is pressed down against surface 310. Beingheated, it will melt the polymeric materials in this region, and pressform the end skirt. A cutting or trimming operation can be used to formskirt 54 in the configuration FIG. 7.

Alternate Embodiment-Reverse Flow Arrangements

Certain techniques according to the present invention can be utilized inreverse flow arrangements. This is illustrated in FIG. 10, which is across-sectional view of a reverse flow arrangement involving principlesaccording to the present invention.

In general the reverse flow filter arrangement is one wherein thefiltering air flows from the inside of the filter directed toward theoutside, as indicated by arrows 400, FIG. 10. Referring to FIG. 10,filter element construction 401 includes an inner, removable andreplaceable filter 405 and an outer, rigid, filter 406. The inner,removable and replaceable filter 405 generally comprises depth media inthe form of a cylinder, and may have either an open end at its bottom,or a closed end. It may be viewed as a form of sock filter. The outerfilter 406 comprises a cylindrical pleated paper filter element havingend caps 407 and 408. The particular element 406 shown has mediacomprising pleated paper 409 extending between end caps 407 and 408. Theouter filter 406 also includes inner and outer liners 410 and 411. Thepleated paper, and inner and outer liners, are potted or embedded in theend caps 407 and 408.

For the arrangement of FIG. 10, the outer rigid filter 406 has a closedend 415 and an open end 416. Air to be filtered is passed through openend 416 and into interior chamber 417 of the outer filter. The innerremovable and replaceable filter 405 is positioned within inner chamber417, so that air to be filtered passes through the filter 405 before itpasses through the rigid outer filter 406. It will be understood thatafter a period of use, the inner filter 405 can be removed and replaced.The inner filter may generally comprise a compressible cylindricalconstruction, and may include multiple layers of depth media. Choices ofmaterial for the inner filter 406 will generally be made utilizing thesame principles as discussed above for the removable and replaceableouter sleeve filter in the arrangements of FIGS. 1-8. Similarly, thematerials chosen for the outer filter 406 may be generally selectedunder the same guiding principles as discussed above with respect to theinner filter of the embodiment of FIGS. 1-8. In some instances the holein end cap 416 though which the inner filter 405 is inserted during usemay have a smaller inside diameter, than the outside diameter of theinner filter 405, when it is expanded. This is permissible, since theinner filter is preferably made from a collapsible material, so that itcan be collapsed, inserted through open end 416, and then be expandedfor preferred positioning.

For the particular arrangement depicted in FIG. 10, it is foreseen thatsealing of the element within a housing will be by engagement with outerperipheral rim 420 of end cap 407. When this is to be done, the materialof end cap 407 is preferably a soft compressible polyurethane materialsimilar to that described above with respect to radial seals in FIGS.1-8, and can be compressed into an appropriately sized rim in a housing,to provide sealing. While alternate sealing arrangements are feasible,the O.D. radial seal described is particularly convenient and easy toeffect.

Some Variations Using the Principles of the Present Invention

From the discussions above, and the variations reflected in thedrawings, it will be apparent that principles according to the presentinvention may be applied in a wide variety of applications and with avariety of structures. For example, as indicated, the removable andreplaceable filtering component can be constructed from a variety ofmaterials and in a variety of configurations. It can be constructed fromdepth media, agglomerating media, high efficiency media, or somecombination. It may be provided as a gradient filter, to advantage. Itmay include a scrim liner thereon, for retention of a desirableconfiguration and shape, and to facilitate mounting.

The filter construction can be arranged so that the removable andreplaceable filter is a sleeve, or an internally received component.

In some arrangements it may be desirable to utilize a reinforcingstructure to support the removable and replaceable filter component.Consider for example the arrangement shown in FIG. 8. It is conceivablethat a useful variation would be to construct the arrangement so thatthe cover 86 includes structural components thereon which project wellinto region 92. In use, the filter sleeve could be secured to thestructure on the cover, and be supported thereby. Thus, when the coveris placed on the housing, the structure would project around theinternally received rigid filter 1 and would support the outer filtersleeve 50.

In some arrangements, means for securing the open end of the sleeve,corresponding to ends 65, 66 in FIG. 6, to the adjacent end cap,corresponding to end cap 3 in FIG. 6, can be provided. For example, aband or clamp could be used around the outer circumference of the sleeveto secure the sleeve to the end cap in this location. With such anarrangement, generally it would be required that, to change theremovable and replaceable outer sleeve, the entire filter assembly canbe dismounted from the housing. Although this loss of advantage would beassociated with such constructions, other advantages described hereinwould still be obtained.

Of course it is foreseen that a variety of geometric configurationscould be used for: the rigid filter element, for example inner element 1of FIG. 1; the removable and replaceable filter sleeve, for examplesleeve 50, FIG. 3; and, the housing. Non-cylindrical constructions, forexample, could be used for any or all of the components, in somesystems. There is no particular reason, for example, why a cross-sectionof both the inner and outer surface of sleeve 50 must be circular. Acircular inner cross-section to facilitate snug fit with an inner filtermember 1 of circular outer cross-section may be desirable. However, withsuch an arrangement, a non-circular outer surface to sleeve 50 couldalso be used, to correspond to a housing having a different internalcross-section than circular.

EXAMPLES

The following example provides further guidance to application ofprinciples according to the present invention.

A typical filter element construction, according to the presentinvention, made for use in a city delivery type of truck, to replace aDonaldson P52-2606 filter element, designed to handle a flow of 500-600CFM (cubic feet per minute), would be as follows:

The internal filter element would generally be configured as shown inFIGS. 1-3. The outside diameter of the open end cap 3 would be about 7-8inches. The inside diameter of end cap 3 would be about 6 inches, at theupper surface 20, and would decrease to about 5.25 inches at itsnarrowest point, FIG. 6. The total thickness of the portion of end cap 3which forms the radial seal, at its thickest point, i.e. along region32, would be about 0.435 inches. The end cap material for end cap 3would be a foamed polyurethane, as described hereinabove.

The second end cap 4 would preferably comprise hard urethane, asdescribed hereinabove. It would preferably be about 0.31 inch thick andhave an outside diameter of about 7.5 inches. The outside diameter wouldextend or project about 0.125 inch beyond the outer liner 9.

The pleated paper 6 would have about 0.625 inch pleats and wouldpreferably be an oil-pleated paper media, in particular an oil treatedhigh perm cellulose. It would be constructed about 12 inches long and ina cylindrical configuration having an inside diameter of about 6 inches.Preferably there would be about 12 pleats per inch, around the outsidediameter. The inner liner would comprise expanded metal.

The outer sleeve 50 would comprise four layers of depth media in aninternal scrim. The outermost layer would be about 0.3 inch deep andcomprise Kem-Wove 4.2 or its functional (filtering) equivalent. The nextinner layer would be about 0.3 inch deep and comprise Kem-Wove 8643 orits functional (filtering) equivalent. The outer two layers would besecured to one another with 3M Super 77.

The inner two layers of depth media would each comprise a layer about0.2 inch deep of AF18. The innermost layer would be lined along itsinside surface with a REEMAY 2011 scrim. The inner layer and scrim wouldbe bonded to one another with 3M Super 77.

When constructed as described above, the filter element constructionwould be sized and shaped appropriately to fit within a conventionalDonaldson EP G110138, EP G110118, EP G11014008, EP G110158 housing.

What is claimed is:
 1. An air filter arrangement for filteringparticulate matter from incoming air to an engine air intake; saidarrangement comprising:(a) a first construction having an upstreamside;(i) said construction comprising first and second end caps withfilter media extending therebetween; said construction including aninner cylindrical liner; said first end cap having a central air flowaperture therein; (b) a removable and replaceable sleeve filter of mediapositioned in covering relation to said first construction upstreamside; said removable and replaceable sleeve filter including:(i) anoutermost layer of media comprising fibrous depth media having a firstefficiency for filtering; (ii) a second layer of media downstream fromsaid outermost layer; said second layer of media having an efficiencyfor filtering which is different from said outermost layer; and, (iii)said outermost layer and said second layer being secured together toform a removable and replaceable sleeve filter; said sleeve filter beingcontinuous and without a nonpermanent seam.
 2. An air filter arrangementaccording to claim 1 wherein:(a) said second layer has a greaterefficiency for filtering than said outermost layer.
 3. An air filterarrangement according to claim 1 wherein:(a) said second layer comprisesfibrous depth media.
 4. An air filter arrangement according to claim 1wherein:(a) said outermost layer has a percent solidity, free state,within the range of about 0.8-1.4%.
 5. An air filter arrangementaccording to claim 1 wherein:(a) said outermost layer comprises fibrousdepth media which includes a blend of fiber sizes.
 6. An air filterarrangement according to claim 5 wherein:(a) said blend of fiber sizescomprises a blend of fiber sizes within the range of 1.5-6.0 denier. 7.An air filter arrangement according to claim 5 wherein:(a) saidoutermost layer comprises polyester fibers.
 8. An air filter arrangementaccording to claim 7 wherein:(a) said outermost layer has a thickness ofabout 0.2-0.75 inches.
 9. An air filter arrangement according to claim 8wherein:(a) said second layer has a thickness of about 0.15-0.4 inches.10. An air filter arrangement according to claim 8 wherein:(a) saidfirst construction comprises a cylindrical media construction whereinsaid first and second end caps are circular.
 11. An air filterarrangement according to claim 10 wherein:(a) said first constructioncomprises a cylindrical extension of pleated media embedded in, andextending between, said first and second end caps.
 12. An air filterarrangement according to claim 11 wherein:(a) said cylindrical extensionof pleated media comprises pleated paper media.
 13. An air filterarrangement according to claim 12 wherein:(a) said pleated paper mediacomprises oil treated cellulose media.
 14. An air filter arrangementaccording to claim 12 wherein:(a) said first construction and saidremovable and replaceable sleeve filter are constructed and arranged towithstand, when assembled, a limiting pressure drop thereacross of atleast about 20 inches of water, without structural collapse and failure.15. An air filter arrangement according to claim 12 wherein:(a) saidpleated media has a pleat depth of at least 0.375 inches.
 16. An airfilter arrangement according to claim 15 wherein:(a) said first end caphas an outer diameter of 4.5 to 13 inches.
 17. An air filterconstruction according to claim 15 wherein:(a) said first constructionincludes an outer liner; and, (b) said removable and replaceable sleevefilter is of an appropriate size to cover said outer liner.
 18. An airfilter construction according to claim 17 wherein:(a) said outer linercomprises a metal liner.
 19. An air filter construction according toclaim 18 wherein:(a) said removable and replaceable sleeve filter isconstructed and arranged for operational collection therein of at least90%, by weight, of particulates collected by said air filter arrangementin use.
 20. An air filter construction according to claim 19 wherein:(a)said outermost layer is constructed and arranged to store 70-90%, byweight, of airborne particles which pass into the filter arrangement,during a lifetime of normal use for the removable and replaceable sleevefilter.
 21. An air filter construction according to claim 1 wherein:(a)said second end cap is a closed end cap with no air flow aperturetherethrough.
 22. An air filter construction according to claim 1wherein:(a) said outermost layer has a percent solidity, free state,within the range of about 0.55-1.4%.